The present invention relates to the design of electronic circuits and, more particularly to electronic circuits, such as negative resistance amplifiers employing feedback techniques.
It is well known that electron triodes such as vacuum tubes, bipolar transistors and MOSFETs are capable of amplification of signal, but along with amplification, they also provide unidirectionality of signal in the circuit
The unidirectionality of an electron triode is based on the conversion mechanism of the information carrier inside the triode. The input voltage signal is converted to the triode current, and the current is converted back to the output voltage at the output node by accumulating it in the output capacitor. The voltage to current conversion mechanism is unidirectional. By forcing current into the triode from the output it never generates voltage at the input electrode. This voltage to current back to voltage conversion creates signal unidirectionality along with the gain of the amplifier. mechanisms are well integrated in the triode, the importance of unidirectionality all by itself has not been well recognized.
As a fundamental matter, the two concepts of amplification and unidirectionality are different concepts. There are amplifying devices that do not have unidirectionality, such as the S-type negative resistance diodes (e.g., a PNPN diode) and the N-type negative resistance diodes (e.g., a tunnel diode). In addition, there are devices such as a microwave isolator or a gyrator which have unidirectionality but no amplification. Yet amplification and unidirectionality have a common character in that they occur only in exceptional circumstances. This is the reason why any idea of generating amplification or unidirectionality is important.
Amplification is characterized by gain. For amplification to be real, the gain must be higher than unity. As for unidirectionality no such clear measure seems to exist. Practically, unidirectionality can be measured only relatively and only partial unidirectionality is realizable in triode circuits.
It is widely known in the art that the unidirectionality mechanisms that exist in electronics and in related areas where the equivalent circuit model is able to describe the dynamic phenomena (examples of such areas are hydraulics logic and bio-logical data processing system consisting of neurons) are as follows: (1) by information carrier conversion (e.g., an electron triode); (2) by burnout mechanisms (e.g., action potential propagation in neurons); (3) by directed transport (e.g., charge coupled devices (CCDs) and parametron logic). Nevertheless, it has been impossible to exhaustively classify the unidirectionality mechanism from these small number of examples.
One device that is well known in the prior art with unidirectionality is the magnetic amplifier that is obsolete today but was used in the past before the 1920s. A magnetic amplifier consists of a transformer having a saturable core 100 is shown in FIG. 1(a). The primary is driven by a DC control current I1, that creates a magnetic flux "PHgr" by both I1 and I2, and "PHgr" is a linear function of both. The primary winding 105 has a large number of turns. As I1 increases, the magnetic core saturates by the primary current magnetomotive force only, and "PHgr" cannot increase any more than the maximum schematically shown in FIG. 1(b). The secondary winding 110 is driven by AC. The impedance looking into the secondary is inductive. If I1 is small, the inductance of the secondary is high. As I1 is increased, however, the core is saturated by the primary magnetomotive force only, and if the AC drive of the secondary is unable to release the core from saturation in any phase of the secondary AC current, the inductance ideally becomes zero. Thus, small primary current is able to control large secondary current. To obtain an ideal operation, it is necessary to keep the series resistance of the secondary winding small. Here, we assume that the copper loss, familiar to one of ordinary skill in the art, is negligible.
The magnetic amplifier is used to amplify signal as follows. The secondary 110 is driven by an AC current source, and the AC voltage developed across the secondary 110 is rectified to recover the low-frequency component that represents the signal. The signal is DC-like, varying slowly compared with the AC power source.
A magnetic amplifier as it is shown in FIG. 1 is not unidirectional. The AC current that drives the secondary 110 generates an AC voltage at the primary terminal. If a magnetic amplifier has high gain, small primary current should be able to create large magnetic flux in the core. This means that the number of turns of the primary 105 must be large, and the number of turns of the secondary 110 is small. Since the AC voltage of the secondary is stepped up to the primary, the AC voltage influences the primary control circuit via the electrical nonlinearity. This is a reverse signal flow through the magnetic amplifier. The primary 105 cannot be by-passed by a capacitor, since that reflects back to the secondary 110. This reverse signal flow can be prevented as follows. As shown in FIG. 2, if two identical nonlinear transformers are connected in series in the primary, and in polarity-inverted series in the secondary, the induced AC voltages at the two primaries cancel, and the reverse signal flow does not occur. This circuit is unidirectional due to clever feedback compensation.
Although methods for achieving unidirectionality with magnetic amplifiers are well known in the art, achieving such unidirectionality in conventional electronic circuitry is not known in the prior art. For example, in a negative resistance amplifier circuit, the input signal source and the amplifier load are directly connected through a two-terminal negative resistance device, and they interact directly. Since the signal flows in either direction, the amplifier circuit is not unidirectional. Thus, there is a need to achieve unidirectionality in conventional electronic circuits such as negative resistance amplifiers.
Generally, a method for creating signal unidirectionality in electronic circuits is disclosed. The methods described below achieve unidirectionality in an electronic circuit by isolating the input signal source from the rest of the circuit.
This invention describes methods for achieving unidirectionality in an electronic circuit with an input side having a signal source and an output side with a load comprising detecting the current passing through the load on the output side, bypassing a portion of the current passing through the load on the output side, and feeding the bypassed portion of the current on the output side to the input side to achieve unidirectionality. Specifically, unidirectionality in an electronic circuit is accomplished by applying feedback such that the impedance looking into the input of the amplifier is increased. These methods are particularly applicable to negative resistance amplifier circuits.
The amount of unidirectionality is varied by controlling the amount of the bypassed portion of the current passing through the load on the output side. The amount of feedback current can be controlled by the specific design of the elements of the circuit. For instance, the amount of unidirectionality in the circuit may be set to a stable level by reducing the size of the impedances on the input side by a fixed amount compared to the impedances on the output side.
A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings.